Hypereosinophilic (hy-per-ee-o-SIN-o-phil-ik) syndrome (HES) refers to a group of blood disorders that occur when you have high numbers of eosinophils — white blood cells that play an important role in your immune system. Over time, these high numbers of eosinophils enter various tissues, causing inflammation and eventually damaging your organs, most commonly targeting the skin, lung, heart, blood and nervous system. Hypereosinophilic syndrome can become life-threatening if not treated.

HES can affect anyone, but it occurs more often in men, usually between 20 and 50 years of age. Symptoms of HES vary, depending on what part of your body is affected. Skin symptoms include itching and rashes, for example. If your lungs are affected, you may be short of breath and have a cough.

Multidisciplinary team of specialized experts. Your Mayo Clinic team may include specialists in allergic diseases, dermatology, gastroenterology, pediatrics, neurology, endocrinology, hematology and pathology.

Experience. Each year, doctors at Mayo Clinic treat more than 840 people with eosinophilia, including hypereosinophilic syndrome.

Expertise. Mayo Clinic's mission is to research and share medical advancements and treatments. The Allergic Diseases Research Laboratory has been actively studying eosinophil biology for almost 50 years, aiming to understand the role of eosinophils in diseases such as hypereosinophilic syndrome. The Allergic Diseases Research Laboratory has had a National Institutes of Health grant in allergic diseases since the 1980s and provides training for doctors from many medical disciplines, with the goals of finding new treatments and eventually curing diseases such as hypereosinophilic syndrome.

Care that revolves around you. At Mayo Clinic, a detailed itinerary for appointments, tests and procedures lets you make the most of your time at the clinic. Mayo Clinic technicians run all tests and labs themselves, which means tests taken in the morning can often be reviewed the same afternoon. Mayo's collaborative approach means two or three days often yields the same diagnosis and care insights that could take weeks in less-coordinated institutions.

The initial goal in diagnosing hypereosinophilic syndrome is to rule out other disorders that can elevate your eosinophil count — such as a parasitic infection, allergic disease, drug reaction or autoimmune disorder. Therefore, provide your doctor with your travel history and a list of medications you're taking.

Ruling out other conditions

Based on your symptoms, your doctor will recommend certain tests. Some tests to rule out other conditions include:

Determining the cause of your HES

If you've been diagnosed with HES, these tests may help determine the cause:

Blood screening. This test can reveal a genetic mutation known as FIP1L1-PDGFRA, which can cause hypereosinophilic syndrome.

Bone marrow biopsy. If your blood screen is negative for a genetic mutation, this test may be considered. Biopsies are also useful because they help exclude the possibility of other conditions.

The goal of treatment for hypereosinophilic syndrome is to reduce the numbers of eosinophils in your body and prevent tissue damage, especially to your heart. Your treatment depends on your symptoms, the severity of your condition and the cause of your HES.

Watchful waiting. If you have no symptoms and your eosinophil count is low enough, your doctor may opt for a "wait and see" approach. Your condition will then be closely monitored for any changes related to HES.

Prednisone. Generally, if you don't have the FIP1L1-PDGFRA gene mutation, you'll initially be treated with prednisone, a corticosteroid, which is gradually tapered to the lowest dose that controls the eosinophil count. If a high dose of prednisone is needed, steroid-sparing medications are added to avoid the side effects. Prednisone side effects may include mood swings, high blood pressure and increased risk of infections.

Protein-tyrosine kinase inhibitor. If you have the FIP1L1-PDGFRA gene mutation, you have, by definition, chronic eosinophilic leukemia. You'll need treatment with imatinib mesylate (Gleevec), a type of drug known as a protein-tyrosine kinase inhibitor. Imatinib mesylate slows the growth of cancer cells and is almost 100 percent effective, especially for men.

Mayo Clinic works with hundreds of insurance companies and is an in-network provider for millions of people. In most cases, Mayo Clinic doesn't require a physician referral. Some insurers require referrals or may have additional requirements for certain medical care. All appointments are prioritized on the basis of medical need.

Doctors trained in allergic diseases treat people with hypereosinophilic syndrome at Mayo Clinic's campus in Arizona.

For appointments or more information, call the Central Appointment Office at 800-446-2279 (toll-free) 8 a.m. to 5 p.m. Mountain Standard Time, Monday through Friday or complete an online appointment request form.

Doctors trained in eosinophil biology and other areas conduct basic and clinical research in potential diagnostic tests and treatments for hypereosinophilic syndrome. Staff in the Allergic Diseases Research Laboratory at Mayo Clinic's campus in Minnesota conduct research in hypereosinophilic syndrome and other eosinophil-related disorders.

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